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| + | *[[Janus kinase 3D structures|Janus kinase 3D structures]] | ||
== References == | == References == | ||
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Revision as of 15:31, 22 December 2021
Human JAK2 JH1 domain in complex with Baricitinib
Structural highlights
Disease[JAK2_HUMAN] Note=Chromosomal aberrations involving JAK2 are found in both chronic and acute forms of eosinophilic, lymphoblastic and myeloid leukemia. Translocation t(8;9)(p22;p24) with PCM1 links the protein kinase domain of JAK2 to the major portion of PCM1. Translocation t(9;12)(p24;p13) with ETV6. Defects in JAK2 are a cause of susceptibility to Budd-Chiari syndrome (BDCHS) [MIM:600880]. A syndrome caused by obstruction of hepatic venous outflow involving either the hepatic veins or the terminal segment of the inferior vena cava. Obstructions are generally caused by thrombosis and lead to hepatic congestion and ischemic necrosis. Clinical manifestations observed in the majority of patients include hepatomegaly, right upper quadrant pain and abdominal ascites. Budd-Chiari syndrome is associated with a combination of disease states including primary myeloproliferative syndromes and thrombophilia due to factor V Leiden, protein C deficiency and antithrombin III deficiency. Budd-Chiari syndrome is a rare but typical complication in patients with polycythemia vera. Defects in JAK2 are a cause of polycythemia vera (PV) [MIM:263300]. A myeloproliferative disorder characterized by abnormal proliferation of all hematopoietic bone marrow elements, erythroid hyperplasia, an absolute increase in total blood volume, but also by myeloid leukocytosis, thrombocytosis and splenomegaly.[1] [2] [3] [4] Defects in JAK2 gene may be the cause of thrombocythemia type 3 (THCYT3) [MIM:614521]. A myeloproliferative disorder characterized by elevated platelet levels due to sustained proliferation of megakaryocytes, and frequently lead to thrombotic and haemorrhagic complications.[5] [6] Defects in JAK2 are a cause of myelofibrosis (MYELOF) [MIM:254450]. Myelofibrosis is a disorder characterized by replacement of the bone marrow by fibrous tissue, occurring in association with a myeloproliferative disorder. Clinical manifestations may include anemia, pallor, splenomegaly, hypermetabolic state, petechiae, ecchymosis, bleeding, lymphadenopathy, hepatomegaly, portal hypertension. Defects in JAK2 are a cause of acute myelogenous leukemia (AML) [MIM:601626]. AML is a malignant disease in which hematopoietic precursors are arrested in an early stage of development.[7] Function[JAK2_HUMAN] Non-receptor tyrosine kinase involved in various processes such as cell growth, development, differentiation or histone modifications. Mediates essential signaling events in both innate and adaptive immunity. In the cytoplasm, plays a pivotal role in signal transduction via its association with type I receptors such as growth hormone (GHR), prolactin (PRLR), leptin (LEPR), erythropoietin (EPOR), thrombopoietin (THPO); or type II receptors including IFN-alpha, IFN-beta, IFN-gamma and multiple interleukins. Following ligand-binding to cell surface receptors, phosphorylates specific tyrosine residues on the cytoplasmic tails of the receptor, creating docking sites for STATs proteins. Subsequently, phosphorylates the STATs proteins once they are recruited to the receptor. Phosphorylated STATs then form homodimer or heterodimers and translocate to the nucleus to activate gene transcription. For example, cell stimulation with erythropoietin (EPO) during erythropoiesis leads to JAK2 autophosphorylation, activation, and its association with erythropoietin receptor (EPOR) that becomes phosphorylated in its cytoplasmic domain. Then, STAT5 (STAT5A or STAT5B) is recruited, phosphorylated and activated by JAK2. Once activated, dimerized STAT5 translocates into the nucleus and promotes the transcription of several essential genes involved in the modulation of erythropoiesis. In addition, JAK2 mediates angiotensin-2-induced ARHGEF1 phosphorylation. Plays a role in cell cycle by phosphorylating CDKN1B. Cooperates with TEC through reciprocal phosphorylation to mediate cytokine-driven activation of FOS transcription. In the nucleus, plays a key role in chromatin by specifically mediating phosphorylation of 'Tyr-41' of histone H3 (H3Y41ph), a specific tag that promotes exclusion of CBX5 (HP1 alpha) from chromatin.[8] [9] [10] [11] Publication Abstract from PubMedCRLF2-rearranged (CRLF2r) acute lymphoblastic leukemia (ALL) comprises over half of Philadelphia chromosome-like (Ph-like) ALL, is associated with poor outcome in children and adults. Overexpression of CRLF2 results in activation of JAK-STAT and parallel signaling pathways in experimental models, but existing small molecule inhibitors of Janus kinases show variable and limited efficacy. Here we evaluated the efficacy of proteolysis-targeting chimeras (PROTACs) directed against Janus kinases. Solving the structure of type I JAK inhibitors ruxolitinib and baricitinib bound to the JAK2 tyrosine kinase domain enabled the rational design and optimization of multiple series of cereblon (CRBN)-directed JAK PROTACs utilizing derivatives of JAK inhibitors, linkers and CRBN-specific molecular glues. The resulting JAK PROTACs were evaluated for target degradation, and activity tested in a panel of leukemia/lymphoma cell lines and xenograft models of kinase-driven ALL. Multiple PROTACs were developed that degraded Janus kinases and potently killed CRLF2--rearranged cell lines, the most active of which also degraded the known CRBN neosubstrate GSPT1, and suppressed proliferation of CRLF2-rearranged ALL in vivo. While dual JAK/GSPT1-degrading PROTACs were most potent, development and evaluation of multiple PROTACs in an extended panel of xenografts identified a potent JAK2-degrading GSPT1-sparing PROTAC that demonstrated efficacy in the majority of the kinase-driven xenografts which were otherwise unresponsive to type I JAK inhibitors. Together, these data show the potential of JAK-directed protein degradation as a therapeutic approach in JAK-STAT-driven ALL, and highlight the interplay of Janus kinase and GSPT1 degradation activity in this context. Degradation of Janus kinases in CRLF2-rearranged acute lymphoblastic leukemia.,Chang Y, Min J, Jarusiewicz J, Actis M, Bradford SY, Mayasundari A, Yang L, Chepyala D, Alcock LJ, Roberts KG, Nithianantham S, Maxwell D, Rowland L, Larsen R, Seth A, Goto H, Imamura T, Akahane K, Hansen B, Pruett-Miller SM, Paietta EM, Litzow MR, Qu C, Yang JJ, Fischer M, Rankovic Z, Mullighan CG Blood. 2021 Jun 10. pii: 476126. doi: 10.1182/blood.2020006846. PMID:34110416[12] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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